TAP and auxiliary circuitry with auxiliary output multiplexer and buffers

ABSTRACT

The present disclosure describes novel methods and apparatuses for directly accessing JTAG Tap domains that exist in a scan path of many serially connected JTAG Tap domains. Direct scan access to a selected Tap domain by a JTAG controller is achieved using auxiliary digital or analog terminals associated with the Tap domain and connected to the JTAG controller. During direct scan access, the auxiliary digital or analog terminals serve as serial data input and serial data output paths between the selected Tap domain and the JTAG controller.

CROSS REFERENCE TO RELATED PATENTS

This application is a divisional of application Ser. No. 14/837,786,filed Aug. 27, 2015, now U.S. Pat. No. 9,519,025, issued Dec. 13, 2016;

Which was a divisional of prior application Ser. No. 14/189,444, filedFeb. 25, 2014, now U.S. Pat. No. 9,146,272, granted Sep. 29, 2015;

Which was a divisional of prior application Ser. No. 13/782,585, filedMar. 1, 2013, now U.S. Pat. No. 8,713,390, granted Apr. 29, 2014;

Which was a divisional of prior application Ser. No. 13/439,454, filedApr. 4, 2012, now U.S. Pat. No. 8,412,995, granted Apr. 2, 2013;

Which was a divisional of prior application Ser. No. 13/039,517, filedMar. 3, 2011, now U.S. Pat. No. 8,176,374, granted May 8, 2012;

Which was a divisional of prior application Ser. No. 12/712,600, filedFeb. 25, 2010, now U.S. Pat. No. 7,925,943, granted Apr. 12, 2011;

Which was a divisional of prior application Ser. No. 12/055,676, filedMar. 26, 2008, now U.S. Pat. No. 7,698,612, granted Apr. 13, 2010;

which was a divisional of prior application Ser. No. 11/150,891, filedJun. 13, 2005, now U.S. Pat. No. 7,395,471, granted Jul. 1, 2008;

Which claims priority from provisional Application No. 60/580,673, filedJun. 17, 2004.

This application is related to U.S. application Ser. No. 11/015,816,filed Dec. 17, 2004, “JTAG Bus Communication Method and Apparatus”, U.S.application Ser. No. 10/983,256, filed Nov. 4, 2204, “Removable andReplaceable Tap Domain Selection Circuitry”, now U.S. Pat. No.7,200,783, issued Apr. 3, 2007, and U.S. Pat. No. 6,393,081 “PluralCircuit Selection Using Role Reversing Control Inputs”, all of which areincorporated herein by reference.

FIELD OF THE DISCLOSURE

This disclosure relates in general to circuit design and in particularto improvements in the design of IEEE 1149.1 Tap interfaces of devices(such as ICs, cores, and/or other circuits) for enhancing communicationto and from the devices during operations such as, but not limited too,(1) test operations, (2) debug operations, (3) trace operations, (4)emulation operations, (5) in-system-programming operations, and (6)other, as needed, operations.

BACKGROUND OF THE DISCLOSURE

Today the IEEE 1149.1 (JTAG) Test Access Port (Tap) interface is usedfor many different applications. While initially designed to provide aserial test interface on ICs to facilitate board testing, the Tapinterface now serves as a serial interface for additional IEEE standardsfor such things as emulation, trace, and debug (IEEE 5001) of ICs andcores, mixed signal testing (IEEE 1149.4) of ICs and cores, advanced ICto IC interconnect testing (IEEE 1149.6), embedded core testing (IEEE1500), and in-system-programming of circuits in ICs and cores (IEEE1532).

An IC device may contain many embedded 1149.1 based Tap architectures(Tap domains). Some of these TAP domains are associated withintellectual property (IP) core circuit devices within the IC, and serveas access interfaces to test, debug, trace, emulation, andin-system-programming circuitry within the IP cores. Other TAP domainsmay exist in the IC which are not associated with cores but rather tocircuitry in the IC external of the cores. Further, the IC itself willtypically contain a TAP domain for operating IC level test, debug,trace, emulation, and in-system-programming, as well as the boundaryscan register associated with the IC's input and output terminals.

From the above, it is clear that Tap domains are being used in evergrowing numbers in devices, such as ICs and cores, for test, debug,trace, emulation, in-system-programming, and other types of operations.

BRIEF SUMMARY OF THE DISCLOSURE

The present disclosure describes and provides for novel methods andapparatuses for directly accessing a desired Tap Domain in a scan pathof many serially connected Tap Domains. The ability to directly access aselected Tap Domain in a scan path of many Tap Domains allows moreefficient serial access to the selected Tap Domain for test, debug,emulation, programming, and/or other operations.

In one embodiment a Tap domain can selectively operate in daisy-chainedor direct scan access modes by reversing the TCK and TMS input terminalconnections to the Tap domain's Tap controller, and reusing auxiliarydigital terminals for direct scan access TDI and TDO terminals. This Tapdomain requires a JTAG controller that can reverse its TCK and TMSoutput terminals and reuse auxiliary digital terminals for direct scanaccess TDI and TDO terminals.

In another embodiment a Tap domain can selectively operate indaisy-chained or direct scan access modes by reversing the TCK and TMSinput terminal connections to the Tap domain's Tap controller 104, andreusing auxiliary analog terminals for direct scan access TDI and TDOterminals. This Tap domain 1502 requires a JTAG controller that canreverse its TCK and TMS output terminals and reuse auxiliary analogterminals for direct scan access TDI and TDO terminals.

In another embodiment a Tap domain can selectively operate in adaisy-chained mode using a first Tap controller and in a direct scanaccess mode using a second Tap controller. Like the earlier Tap domainembodiments, this Tap domain reuses auxiliary digital or analogterminals for direct scan access TDI and TDO terminals. This Tap domainrequires a JTAG controller that can reverse its TCK and TMS outputterminals and reuse auxiliary digital or analog terminals for directscan access TDI and TDO terminals.

In another embodiment a Tap domain can selectively operate indaisy-chained or direct scan access modes by using two separate TMSinput terminals, and reusing auxiliary digital or analog terminals fordirect scan access TDI and TDO terminals. This Tap domain requires aJTAG controller that has two separately controllable TMS outputterminals and can reuse auxiliary digital or analog terminals for directscan access TDI and TDO terminals.

In another embodiment a Tap domain can selectively operate in adaisy-chained or in a simultaneous daisy-chain and direct scan accessmodes. During the simultaneous daisy-chain and direct scan access mode,the daisy-chain access is achieved using the normal TDI and TDOterminals, while the direct scan access is achieved by reusing auxiliarydigital or analog terminals as additional TDI and TDO terminals. ThisTap domain requires a JTAG controller that has a first TDO source fortransmitting data to a first TDO terminal, a second TDO source fortransmitting data to an auxiliary digital or analog terminal used as asecond TDO terminal, a first TDI destination for receiving data from afirst TDI terminal, and a second TDI destination for receiving data froman auxiliary digital or analog terminal used as a second TDI terminal.

While the scan path examples of these embodiments show all the IC/coresin the scan paths as being adapted to include one of the Tap domainembodiments of the present disclosure, that need not be the case. Indeedthe scan paths may include mixtures of IC/cores with adapted andnon-adapted Tap domains. The operation of the present embodiments toprovide direct scan access to a selected and adapted Tap domain in ascan path of Tap domains is independent of whether the scan pathincludes non-adapted Tap domains or not.

BRIEF DESCRIPTION OF THE VIEWS OF THE DRAWINGS

FIG. 1 depicts a conventional JTAG Tap domain including a Tapcontroller, instruction register, and data registers.

FIG. 2 depicts the state diagram of the JTAG Tap controller.

FIG. 3A depicts a JTAG controller coupled to a scan path of ICs/coreseach including a convention Tap domain.

FIG. 3B depicts the JTAG controller of FIG. 3A in more detail.

FIG. 4 depicts an extended Tap domain that includes auxiliary digitalcircuitry and I/O terminals.

FIG. 5A depicts a JTAG controller coupled to a scan path of ICs/coreseach including the Tap domain of FIG. 4.

FIG. 5B depicts the JTAG controller of FIG. 5A in more detail.

FIG. 6 depicts the Tap domain of FIG. 4 adapted according to the presentdisclosure.

FIG. 7A depicts a JTAG controller coupled to a scan path of ICs/coreseach including the Tap domain of FIG. 6 according to the presentdisclosure.

FIG. 7B depicts the JTAG controller of FIG. 7A in more detail accordingto the present disclosure.

FIG. 7C depicts TCK and TMS signal multiplexing in Tap domains of FIG. 6and the JTAG controller of FIG. 7B according to the present disclosure.

FIG. 8 depicts the FIG. 6 Tap domains being controlled by the JTAGcontroller of FIG. 7B to operate in a daisy-chain scan access modeaccording to the present disclosure.

FIGS. 9A-9D illustrate the FIG. 6 Tap domains being controlled by theJTAG controller of FIG. 7B to operate in direct scan access modesaccording to the present disclosure.

FIG. 10 depicts the Tap domain of FIG. 6 transitioning betweendaisy-chain and direct scan access modes according to the presentdisclosure.

FIG. 11 depicts timing of JTAG instruction register scan operationsbeing used to switch Tap domains between daisy-chain and direct scanaccess modes according to the present disclosure.

FIG. 12 depicts timing of JTAG data register scan operations being usedto switch Tap domains between daisy-chain and direct scan access modesaccording to the present disclosure.

FIG. 13 depicts an extended Tap domain that includes auxiliary analogcircuitry and I/O terminals.

FIG. 14A depicts a JTAG controller coupled to a scan path of ICs/coreseach including the Tap domain of FIG. 13.

FIG. 14B depicts the JTAG controller of FIG. 13A in more detail.

FIG. 15 depicts the Tap domain of FIG. 13 adapted according to thepresent disclosure.

FIG. 16A depicts a JTAG controller coupled to a scan path of ICs/coreseach including the Tap domain of FIG. 15 according to the presentdisclosure.

FIG. 16B depicts the JTAG controller of FIG. 16A in more detailaccording to the present disclosure.

FIG. 17 depicts a first alternate method of adapting the Tap domains ofFIGS. 4 and 13 according to the present disclosure.

FIG. 18 depicts the state diagram of one of the Tap controllers in theTap domain of FIG. 17 according to the present disclosure.

FIG. 19 depicts a second alternate method of adapting the Tap domains ofFIGS. 4 and 13 according to the present disclosure.

FIG. 20A depicts a JTAG controller coupled to a scan path of ICs/coreseach including the Tap domain of FIG. 19 according to the presentdisclosure.

FIG. 20B depicts the JTAG controller of FIG. 20A in more detailaccording to the present disclosure.

FIG. 21 depicts a third alternate method of adapting the Tap domains ofFIGS. 4 and 13 according to the present disclosure.

FIG. 22A depicts a JTAG controller coupled to a scan path of ICs/coreseach including the Tap domain of FIG. 21 according to the presentdisclosure.

FIG. 22B depicts the JTAG controller of FIG. 22A in more detailaccording to the present disclosure.

FIG. 23A depicts the FIG. 21 Tap domains being controlled by the JTAGcontroller of FIG. 22B to operate in a daisy-chain scan access modeaccording to the present disclosure.

FIG. 23B depicts the FIG. 21 Tap domains being controlled by the JTAGcontroller of FIG. 22B to operate in a simultaneous daisy-chain anddirect scan access mode according to the present disclosure.

DETAILED DESCRIPTION

FIG. 1 depicts an example of an IEEE 1149.1 Tap domain 102. The Tapdomain includes a Tap controller 104, an instruction register (IR) 106,at least two data registers (DR) 108, multiplexers 110 and 112, testdata output (TDO) register 114. The Tap domain interface consists of atest data input (TDI) input 116 and buffer 118, a test clock (TCK) input120 and buffer 122, a test mode select (TMS) input 124 and buffer 126, atest reset (TRST) input 128 and buffer 130, and a TDO output 132 andbuffer 134. The Tap controller 104 outputs a control bus 136 to the dataand instruction registers 106 and 108, multiplexer 112, output register114, and buffer 134. The instruction register 106 outputs a control bus138 to the data registers 108 and multiplexer 110. In response controlinputs on TCK and TMS the Tap controller 104 outputs control on bus 136to capture data into and shift data through either the IR 106 or aselected DR 108 from TDI to TDO. The data shifted into IR 106 or DR 108is updated and output at the end of the shift operation. In response toa TRST input to the Tap controller 104, the TAP controller, IR 106, andoptionally DRs 108 are reset to known states. The structure andoperation of IEEE 1149.1 Tap domain architectures are well known.

FIG. 2 depicts the state diagram of the Tap controller 104. All IEEE1149.1 standard Tap controllers operate according to this state diagram.State transitions occur on the rising edge of TCK in response to thelogic level applied to the TMS input. The IEEE 1149.1 Tap state diagramis well known.

FIG. 3A depicts an example scan path 302 where a number of Tap domain102 interfaces of ICs 304-310 on a substrate or embedded cores 304-310within an IC are connected together serially, via their TDI 116 and TDO132 terminals. The TDO input 312 and TDO output 314 of the scan path302, along with the TCK 120, TMS 124, and TRST 128 inputs of each TapDomain, are connected to a JTAG Controller 316. The JTAG Controller canserve as a test, debug, trace, emulation, in-system-programming, and/orother application controller. While only four Tap domains 102 ofICs/cores 304-310 are shown, any number of IC/core Tap domains may existin scan path 302, as indicated by dotted line 318.

FIG. 3B depicts an example JTAG Controller 316. The JTAG Controllerconsists of a Tap interface circuit 319 and a computer 320 forcontrolling the Tap interface circuit. The Tap interface circuitincludes a TCK output 322 from a TCK source circuit 324, a TMS output326 from a TMS source circuit 328, a TRST output 330 from controlcircuit 332, a TDO output 334 from a TDO source circuit 336, and a TDIinput 338 to a TDI destination circuit 340. During JTAG instruction ordata scan operations, the computer 320 enables the TCK, TMS, and TDOsources, via control circuitry 332, to output TCK 322 and TMS 326control to the TCK 120 and TMS 124 inputs of the Tap domains of scanpath 302 and TDO 334 data to the TDI 312 input of the scan path 302. TheTDI destination 340 is also enabled, via the control circuitry 332, toreceive TDI 338 data from the TDO output 314 of the scan path 302. TheTap domains in scan path 302 can be reset by the computer enabling thecontrol circuitry 332 to output a logic low on TRST 330 to the TRSTinputs 128 of the Tap domains.

As seen in FIG. 3A, if an instruction or data pattern is to be input toand/or output from a target Tap domain 102 in scan path 302 from JTAGController 316 the pattern must serially pass through all leading and/orfollowing Tap domains 102 in the scan path 302. Thus a data input and/oroutput latency exists between a target Tap Domain in scan path 302 andJTAG Controller 316, due to having to serially traverse intermediate TapDomains. To further exacerbate the problem, the shifting frequency ofthe scan path 302 is limited by the slowest shifting TAP domain in thescan path. For example, if a target Tap Domain (i.e. the one where datais to be input to and/or output from) can shift at 50 MHz, but one ormore of the other Tap Domains that need to be serially traversed duringthe input or output operation can only shift at 10 MHz, the datatransfer between the controller 316 and the target Tap Domain will belimited to the frequency of the slower Tap Domain, i.e. 10 MHz. Due tothe above mentioned data latency and shift frequency limitationproblems, it is clear that the data communication bandwidth between atarget Tap Domain 102 and JTAG Controller 316 is not optimized.

FIG. 4 depicts an example of an IEEE 1149.1 Tap domain 402 which hasbeen extended to include Auxiliary Digital Circuitry 404 and auxiliaryterminals AX1 406 and AX2 408. The AX1 terminal is coupled to theAuxiliary Digital Circuitry via input buffer 410 and output buffer 412.The AX2 terminal is coupled to the Auxiliary Digital Circuitry via inputbuffer 414 and output buffer 420. I/O control signals 418 and 420 fromthe Auxiliary Digital Circuitry regulate the input or output modes ofthe AX1 and AX2 terminals, respectively. While only two auxiliaryterminals AX1 and AX2 are shown, any number could be used. As seen, theAuxiliary Digital Circuitry may be coupled to the Tap control bus 136and instruction register control bus 138 to allow data registers withinthe Auxiliary Digital Circuitry to be accessed via the TDI 116 and TDO132 terminals to load/unload data and/or control information. Tapdomains are extended to include Auxiliary Digital Circuitry andterminals to enable TAP independent data I/O and/orbreakpoint/triggering functions required for embedded debug, emulation,and trace operations. Some standardized examples of using AuxiliaryDigital Circuitry and terminals with a Tap domain are given in IEEEstandard 5001 (Ref 1), and MIPs EJTAG (Ref 2). Other examples includeuse of emulation/trace/debug circuitry and emulation 0 (EMU0) andemulation 1 (EMU1) terminals in Texas Instruments DSP IC/core productfamily. With the exception of the Auxiliary Digital Circuitry andterminals, the Tap domain 402 is similar to Tap Domain 102.

FIG. 5A depicts an example scan path 502 where a number of Tap domain402 interfaces of ICs 504-510 on a substrate or embedded cores 504-510within an IC are connected together serially, via their TDI 116 and TDO132 terminals. The TDO input 312 and TDO output 314 of the scan path502, along with the TCK 120, TMS 124, TRST 128, AX1 406, and AX2 408terminals of each Tap Domain 402, are connected to an Extended DigitalJTAG Controller 516. The JTAG Controller 516 can serve as a test, debug,trace, emulation, in-system-programming, and/or other applicationcontroller.

FIG. 5B depicts an example of an Extended Digital JTAG Controller 516.The JTAG Controller consists of a Tap interface circuit 518 and acomputer 320 for controlling the Tap interface circuit. The Tapinterface circuit 518 is like the Tap interface circuit 318 except thatit includes AX1 520 and AX2 522 I/O terminals for interfacing to the AX1406 and AX2 408 I/O terminals of Tap domains 402, and a DigitalSource/Destination circuit 524. The Digital Source/Destination Circuit524 is used to control the inputting and/or outputting of signalsbetween the controller's AX1 520 and AX2 522 terminals and the AX1 406and AX2 408 terminals of Auxiliary Digital Circuitry of the Tap domains402. The input and/or output operation of the Digital Source/DestinationCircuit 524 is controlled by computer 320 via Control Circuitry 532.

As seen in FIG. 5A, the Extended Digital JTAG controller 516 cancommunicate to the Tap domains 402 using JTAG instruction and datascans, as does the JTAG controller 316 of FIG. 3A. Also, the ExtendedDigital JTAG controller 516 can communicate to the Auxiliary DigitalCircuitry 404 of Tap domains 402 via the AX1 and AX2 terminals 520 and522. As mentioned, the AX1/AX2 communication may be used fortransferring debug, emulation, or trace data or for transferringtrigger/breakpoint signals between the Extended Digital controller 516and the Auxiliary Digital circuitry 404 within the Tap domains.

FIG. 6 depicts an example of an IEEE 1149.1 Tap domain 602 of thepresent disclosure. Tap domain 602 is similar to the Tap domain 402 ofFIG. 4 with the following differences.

The TCK 120, TMS 124, AX1 406, and AX2 408 terminals of FIG. 4 have beenrenamed to TCK/TMS 622, TMS/TCK 624, AX1/TDI 626, and AX2/TDO 628,respectively, to indicate the dual use of the terminals.

A two input multiplexer 604 has been inserted into the TCK/TMS 622 inputpath to the Tap controller 104. One input of the multiplexer 604 iscoupled to the output of TCK/TMS buffer 122, the other input is coupledto the output of TMS/TCK buffer 126, and the output of the multiplexeris coupled to the TCK input of Tap controller 104. The control input tothe multiplexer is connected to a switch control signal 614.

A two input multiplexer 606 has been inserted into the TMS/TMS 624 inputpath to the Tap controller 104. One input of the multiplexer 606 iscoupled to the output of TCK/TMS buffer 122, the other input is coupledto the output of TMS/TCK buffer 126, and the output of the multiplexeris coupled to the TMS input of Tap controller 104. The control input tothe multiplexer is connected to the switch control signal 614.

A two input multiplexer 608 has been inserted into the AX1 I/O controlsignal output path 418 from Auxiliary Digital Circuitry 404. One inputof multiplexer 608 is coupled to the I/O control signal 418, the otherinput is coupled to an OFF signal 630, and the output of the multiplexeris coupled to the 3-state input of AX1/TDI output buffer 412. The OFFsignal is set to a state that disables the output of buffer 412. Thecontrol input to the multiplexer is connected to the switch controlsignal 614.

A two input multiplexer 610 has been inserted into the AX2 I/O controlsignal output path 420 from Auxiliary Digital Circuitry 404. One inputof the multiplexer 610 is coupled to the output of I/O control signal420, the other input is coupled to the TDO output enable signal 632 ofTap controller bus 136 (i.e. the signal that enables the TDO buffer 134during JTAG shift operations), and the output of the multiplexer iscoupled to the 3-state input of AX2/TDO output buffer 416. The controlinput to the multiplexer is connected to the switch control signal 614.

A two input multiplexer 612 has been inserted into the AX2 output signalpath 422 from Auxiliary Digital Circuitry 404. One input of themultiplexer 612 is coupled to the AX2 output signal 422 of AuxiliaryDigital Circuitry 404, the other input is coupled to the output of TDOregister 114, and the output of the multiplexer is coupled to the inputof the AX2/TDO 3-state output buffer 416. The control input to themultiplexer is connected to the switch control signal 614.

A two input multiplexer 616 has been inserted into the TDI input path116. One input of the multiplexer 616 is coupled to the output of TDIbuffer 118, the other input is coupled to the output of the AX1/TDIinput buffer 410, and the output of the multiplexer is coupled to theTDI inputs of the instruction register 106 and data registers 108. Thecontrol input to the multiplexer is connected to the switch controlsignal 614.

The switch control signal 614 can be controlled, by design choice, fromeither a data register 108 output (indicated as dotted line output 618),or an instruction register 106 output (indicated as dotted line output620 from the instruction register output bus 138). If controlled by adata register 108, switch control signal 614 is set high or low by aJTAG data scan operation. If controlled by the instruction register 106,switch control signal 614 is set high or low by a JTAG instruction scanoperation.

In the Tap domain 602 example of FIG. 6, when the switch control signal614 is set low, multiplexer 604 couples the TCK/TMS terminal 622 to theTCK input of Tap controller 104, multiplexer 606 couples the TMS/TCKterminal 624 to the TMS input of Tap controller 104, multiplexer 608couples the AX1 I/O control signal 418 to the 3-state control input ofAX1/TDI buffer 412, multiplexer 610 couples the AX2 I/O control signal420 to the 3-state control input of AX2/TDO buffer 416, multiplexer 612couples the AX2 output signal 422 to the input of AX2 buffer 416, andmultiplexer 616 couples the output of the TDI input buffer 118 to theTDI inputs of the data registers 108 and instruction register 106. Inthis configuration, the Tap domain 602 operates like the Tap domain 402of FIG. 4.

When the switch control signal 614 is set high, multiplexer 604 couplesthe TMS/TCK signal 624 to the TCK input of Tap controller 104,multiplexer 606 couples the TCK/TMS signal 622 to the TMS input of Tapcontroller 104, multiplexer 608 couples the OFF signal 630 to the3-state control input of AX1/TDI buffer 412, multiplexer 610 couples theTDO output enable signal 632 to the 3-state control input of AX2/TDObuffer 416, multiplexer 612 couples the output of TDO register 114 tothe input of AX2/TDO buffer 416, and multiplexer 616 couples the outputof AX1/TDI buffer 410 to the TDI inputs of the data registers 108 andinstruction register 106. In this configuration, the Tap domain 602departs from the operation mode of Tap domain 402 of FIG. 4 and entersthe direct scan access operation mode of the present embodiment.

FIG. 7A depicts an example scan path 702 where a number of Tap domain602 interfaces of ICs 704-710 on a substrate or embedded cores 704-710within an IC are connected together serially, via their TDI 116 and TDO132 terminals. The TDO input 312 and TDO output 314 of the scan path702, along with the TCK/TMS 622, TMS/TCK 624, TRST 128, AX1/TDI 626, andAX2/TDO 628 terminals of each Tap Domain 602, are connected to anExtended Digital JTAG Controller with Direct Scan Access 716. The JTAGController 716 can serve as a test, debug, trace, emulation,in-system-programming, and/or other application controller. The JTAGcontroller 716 can access these applications using the conventional JTAGdaisy-chain approach or the direct scan access approach of the presentembodiment.

FIG. 7B depicts an example of an Extended Digital JTAG Controller withDirect Scan Access 716. The JTAG Controller 716 consists of a Tapinterface circuit 718 and a computer 320 for controlling the Tapinterface circuit. The Tap interface circuit 718 is like the Tapinterface circuit 518 of FIG. 5B with the following differences.

The TCK 322, TMS 326, AX1 520, and AX2 522 terminals of the controllerof FIG. 5B have been renamed to TCK/TMS 724, TMS/TCK 726, AX1/TDO 720,and AX2/TDI 722, respectively, to indicate the dual use of the terminalsby the present embodiment. The TCK/TMS terminal 724 couples to theTCK/TMS terminals 622 of Tap domains 602. The TMS/TCK terminal 726couples to the TMS/TCK terminals 624 of Tap domains 602. The AX1/TDOterminal 720 couples to the AX1/TDI terminals 626 of Tap domains 602.The AX2/TDI 722 terminal couples to the AX2/TDO terminals of Tap domains602. The TDO 334, TDI 338, and TRST 330 terminals are coupled to TapDomain 602 terminals TDI 116, TDO 132, and TRST 128 respectively.

A two input multiplexer 728 has been inserted into the TCK/TMS 724output path. One input of the multiplexer is coupled to the output ofTCK Source 324, the other input is coupled, via delay circuit 736, tothe output of TMS Source 328, and the output of the multiplexer iscoupled to the TCK/TMS terminal 724. The control input to themultiplexer is connected to control signal 740 from Control Circuitry738.

A two input multiplexer 730 has been inserted into the TMS/TCK 726output path. One input of the multiplexer is coupled to the output ofTCK Source 324, the other input is coupled to the output of TMS Source328, and the output of the multiplexer is coupled to the TMS/TCKterminal 726. The control input to the multiplexer is connected tocontrol signal 740 from Control Circuitry 738.

A two input multiplexer 732 has been inserted into the TDI 338 inputpath. One input of the multiplexer is coupled to the TDI 338 terminal,the other input is coupled to the AX2/TDI 722 terminal, and the outputof the multiplexer is coupled to the TDI Destination 340. The controlinput to the multiplexer is connected to control signal 740 from ControlCircuitry 738.

A two input multiplexer 734 has been inserted into the AX1/TDO 720output path. One input of the multiplexer is coupled to the output ofTDO Source 336, the other input is coupled to the output of DigitalSource/Destination 524, and the output of the multiplexer is coupled tothe AX1/TDO 720 terminal. The control input to the multiplexer isconnected to control signal 740 from Control Circuitry 738.

Control Circuitry 738 provides, in addition to the functionality ofControl Circuitry 532, the control signal 740 for regulating thesettings of multiplexers 728-734, in response to input from computer320.

As seen in the Tap interface circuit 718 example of FIG. 7B, when thecontrol signal 740 is set low the multiplexers 728-734 are controlledsuch that the TCK source 324 is coupled to the TCK/TMS terminal 724, theTMS source 328 is coupled to the TMS/TCK terminal 726, the TDIDestination 340 is coupled to the TDI terminal 338, and the DigitalSource/Destination 524 is coupled to the AX1/TDO terminal 720. In thismode, the Tap Interface Circuit 718 operates the same as the TapInterface Circuit 518 of FIG. 5B to access the Tap domains 602 of scanpath 702 in a daisy-chain fashion.

When the control signal 740 is set high the multiplexers 728-734 arecontrolled such that the TMS source 328 is coupled to the TCK/TMSterminal 724, the TCK source 324 is coupled to the TMS/TCK terminal 726,the TDI Destination 340 is coupled to the AX2/TDI terminal 722, and theTDO source 336 is coupled to the AX1/TDO terminal 720. In this mode, theTap Interface Circuit 718 operates to access the selected Tap domain 602using the direct scan access approach of the present embodiment. Theselected Tap domain 602 will be configured for direct scan access by itsSwitch Control signal 614 being set high. Non-selected Tap domains 602will remain in the daisy-chain TDI to TDO access mode by their SwitchControl signal 614 being set low. During direct scan access, theselected Tap domain 602 will input serial data at its AX1/TDI terminal626 from the AX1/TDO terminal 720 of JTAG controller 716, and willoutput serial data from its AX2/TDO terminal 628 to the AX2/TDI terminal722 of the JTAG controller 716 during instruction and data scanoperations. Only the selected Tap domain will receive the correct TMSand TCK inputs for performing instruction and data scans. Non-selectedTap domains will receive input on TMS and TCK but the input will notaffect the state of the non-selected Tap domains.

FIG. 7C depicts TMS and TCK control inputs to selected and non-selectedTap domains. Circuit blocks 742, 744, and 746 represent simplifiedportions of Tap domains 602 in IC/Core 704-708 and circuit block 748represents a simplified portion of JTAG controller 716. Each Tap domaincircuit block 742-746 consists of a Tap controller 104 and multiplexers604 and 606. JTAG controller circuit block 748 consists of TCK and TMSsources 324 and 328 and multiplexers 728 and 730. During daisy-chainaccess mode the Switch Control signal 614 of each Tap domain circuitblock 742-746 is set low and the control signal 740 of the JTAGcontroller circuit block is set low. With this setting the multiplexersare configured to allow the TCK source 324 to drive the TCK input ofeach Tap controller 104 and the TMS source 328 to drive the TMS input ofeach Tap controller 104.

When direct scan access of say Tap domain circuit block 744 is desired,its Switch Control signal 614 will be set high and the Control signal740 of the JTAG controller circuit block 748 will be set high. TheSwitch Control signal 614 of the other Tap domain circuit blocks 742 and746 will remain low. In this configuration, the multiplexers of blocks744 and 748 allow the TCK source 324 and TMS source 328 to correctlydrive the TCK and TMS inputs, respectively, of the Tap controller 104 ofblock 744 to perform instruction and data scan operations. The low onthe Switch Control signals 614 to multiplexers 604 and 606 of blocks 742and 746 cause the TCK and TMS inputs of the Tap controllers 104 of thoseblocks to be driven incorrectly by the TMS source 328 and TCK source324, respectively, of JTAG controller block 748. As will be describedlater in regard to the timing diagrams of FIGS. 11 and 12, anincorrectly driven Tap controller 104 will not respond to TCK and TMSinputs, and will remain in the Run Test/Idle state. Thus from FIG. 7C itis seen that the TMS and TCK multiplexing in the Tap domains 742-746 andJTAG controller 748 enable a selected Tap domain to receive the correctJTAG TCK and TMS protocol to perform instruction and data scans whilenon-selected Tap domains receive an incorrect JTAG TCK and TMS protocoland remain inactive in the Run Test/Idle state.

FIG. 8 depicts the JTAG controller 716 performing a daisy-chained JTAGinstruction or data scan operation through Tap domains 602 of ICs/cores704-710 in scan path 702. The instruction 106 or data 108 register ofeach IC/core is indicated by register element 804. Bus 808 includes thecontrol signals between the JTAG controller 716 and Tap controller 104of Tap domains 602. Bus 806 includes the auxiliary digital I/O signalsbetween the JTAG controller 716 and Auxiliary Digital Circuitry 404 ofTap domains 602. In this configuration, the auxiliary digital signalsmay be used to perform conventional data I/O, or trigger/breakpointoperations, such as those described in the previously referenced IEEEStandard 5001.

FIG. 9A depicts scan path 702 configured to perform a direct scan accessoperation between the JTAG controller 716 and an instruction or dataregister within Tap domain 602 of IC/core 704. To achieve this operationthe Switch Control signal 614 in Tap domain 602 of IC/core 704 is sethigh, the Switch Control signals 614 of Tap domains 602 of IC/cores706-710 are set low, and the control signal 740 of the JTAG controller716 is set high. During this direct scan access operation, the Tapcontrollers 104 of Tap domains 602 of IC/cores 706-710 are forced to goto and remain in the Run Test/Idle state. The AX1/TDI 626 and AX2/TDO628 terminals of IC/cores 706-710 are disabled, as indicated by dottedline, to allow the AX1/TDI 626 and AX2/TDO 628 terminals of the selectedIC/core 704 to operate as JTAG TDI and TDO terminals.

FIG. 9B depicts scan path 702 configured to perform a direct scan accessoperation between the JTAG controller 716 and an instruction or dataregister within Tap domain 602 of IC/core 706. To achieve this operationthe Switch Control signal 614 in Tap domain 602 of IC/core 706 is sethigh, the Switch Control signals 614 of Tap domains 602 of IC/cores 704,708, and 710 are set low, and the control signal 740 of the JTAGcontroller 716 is set high. During this direct scan access operation,the Tap controllers 104 of Tap domains 602 of IC/cores 704, 708, and 710are forced to go to and remain in the Run Test/Idle state. The AX1/TDI626 and AX2/TDO 628 terminals of IC/cores 704, 708, and 710 aredisabled, as indicated by dotted line, to allow the AX1/TDI 626 andAX2/TDO 628 terminals of the selected IC/core 706 to operate as JTAG TDIand TDO terminals.

FIG. 9C depicts scan path 702 configured to perform a direct scan accessoperation between the JTAG controller 716 and an instruction or dataregister within Tap domain 602 of IC/core 708. To achieve this operationthe Switch Control signal 614 in Tap domain 602 of IC/core 708 is sethigh, the Switch Control signals 614 of Tap domains 602 of IC/cores 704,706, and 710 are set low, and the control signal 740 of the JTAGcontroller 716 is set high. During this direct scan access operation,the Tap controllers 104 of Tap domains 602 of IC/cores 704, 706, and 710are forced to go to and remain in the Run Test/Idle state. The AX1/TDI626 and AX2/TDO 628 terminals of IC/cores 704, 706, and 710 aredisabled, as indicated by dotted line, to allow the AX1/TDI 626 andAX2/TDO 628 terminals of the selected IC/core 708 to operate as JTAG TDIand TDO terminals.

FIG. 9D depicts scan path 702 configured to perform a direct scan accessoperation between the JTAG controller 716 and an instruction or dataregister within Tap domain 602 of IC/core 710. To achieve this operationthe Switch Control signal 614 in Tap domain 602 of IC/core 710 is sethigh, the Switch Control signals 614 of Tap domains 602 of IC/cores704-708 are set low, and the control signal 740 of the JTAG controller716 is set high. During this direct scan access operation, the Tapcontrollers 104 of Tap domains 602 of IC/cores 704-708 are forced to goto and remain in the Run Test/Idle state. The AX1/TDI 626 and AX2/TDO628 terminals of IC/cores 704-708 are disabled, as indicated by dottedline, to allow the AX1/TDI 626 and AX2/TDO 628 terminals of the selectedIC/core 710 to operate as JTAG TDI and TDO terminals.

FIG. 10 depicts the daisy-chain and direct scan access modes of the Tapdomains 602 of FIGS. 6 through 9. At power up or following a TRST input,the Tap domains 602 will be in the daisy-chain scan mode 1002 and allwill operate together through Tap states to perform instruction and datascan operations as shown in FIG. 8. When direct scan access is desiredto a selected Tap domain 602, the Switch control signal 614 of that Tapdomain will be set high during an instruction or data scan updateoperation (i.e. in the Update-IR or Update-DR states of FIG. 2).

In response to Switch control signal 614 being set high, the Tap domains602 will transition to the Run Test/Idle state. The non-selected Tapdomains 602 will go to the Run Test/Idle state 1010 of the daisy-chainmode 1002 via transition path 1008. The selected Tap domain 602 will goto the Run Test/Idle state 1012 of the direct scan access mode 1004 viatransition path 1006. While the Tap domains are in the Run Test/Idlestate, the control signal 740 of the JTAG controller 716 is set high toissue a correct TCK and TMS protocol to the selected Tap domain 602, andan incorrect TCK and TMS protocol to the non-selected Tap domains 602.

The correct TCK and TMS protocol received by the selected Tap domain 602enables the Tap domains to move from the Run Test/Idle state 1012 toperform direct instruction and data scan access operations, as indicatedin FIGS. 9A-9D. The incorrect TCK and TMS protocol received by thenon-selected Tap domains 602 during the direct scan access of theselected Tap domain 602 causes the non-selected Tap domains to remain inthe Run Test/Idle state 1010, as indicated in FIG. 9A-9D.

Following the completion of the direct scan access of the selected Tapdomain 602, its Switch control signal 614 is set low during theUpdate-IR or Update-DR state of an instruction or data scan operationrespectively. In response the low on the Switch control signal 614, theselected Tap domain transitions to the Run Test/Idle state 1010 to jointhe non-selected Tap domains in the daisy-chain scan mode 1002 asindicated by transition 1014. The Run Test/Idle states 1010 and 1012 areone and the same state. They are shown as separate states only toindicate the state as it would appear when the Tap domains 602 are ineither the daisy-chain or direct scan access modes. After the selectedTap domain has rejoined the non-selected Tap domains in the RunTest/Idle state 1010, the control signal 740 of the JTAG controller 716is set low to again issue a correct TCK and TMS protocol to all Tapdomains 602 in the daisy-chain scan access mode 1002. All Tap domainscan now operate in the daisy-chain scan access mode to performinstruction and data scan operations, as indicated in FIG. 8.

Timing example 1102 of FIG. 11 shows the Tap controller 104 statesequence of an instruction register scan operation being used to set theSwitch Control signal 614 of a selected Tap domain 602 high to switchfrom the daisy-chain scan access mode 1002 to the direct scan accessmode 1004. The Pause indication 1108 in the Run Test/Idle state is wherethe JTAG controller 716 sets the control signal 740 high to allowoutputting the direct scan access TCK and TMS protocol to the selectedTap domain 602.

Timing example 1104 of FIG. 11 shows the Tap controller 104 operating inthe direct scan access mode 1004. Note in the timing that TMS/TCK 624operates as the TCK input to the selected Tap domain and TCK/TMS 622operates as the TMS input to the selected Tap domain. Also, note thatthe delay 1112 between the TCK/TMS and TMS/TCK signals, introduced bythe delay circuit 736 of FIG. 7B, causes all rising edge transitions onthe TCK/TMS signal 622 to occur while the TMS/TCK signal 624 is at alogic low level. Forcing TMS/TCK low during all TCK/TMS rising edgescauses the non-selected Tap domains to remain in the Run Test/Idle stateof FIG. 2. This is the incorrect TCK and TMS protocol previouslymentioned in regard to FIG. 7C.

Timing example 1106 of FIG. 11 shows the Tap controller 104 statesequence of an instruction register scan operation being used to set theSwitch Control signal 614 of the selected Tap domain 602 low to switchfrom the direct scan access mode 1004 to the daisy-chain scan accessmode 1002. The Pause indication 1110 in the Run Test/Idle state is wherethe JTAG controller 716 sets the control signal 740 low to allowoutputting the daisy-chain scan access TCK and TMS protocol to all Tapdomains 602.

Timing example 1202 of FIG. 12 shows the Tap controller 104 statesequence of a data register scan operation being used to set the SwitchControl signal 614 of a selected Tap domain 602 high to switch from thedaisy-chain scan access mode 1002 to the direct scan access mode 1004.Again, the Pause indication 1208 in the Run Test/Idle state is where theJTAG controller 716 sets the control signal 740 high to allow outputtingthe direct scan access TCK and TMS protocol to the selected Tap domain602.

Timing example 1204 of FIG. 12 shows the Tap controller 104 operating inthe direct scan access mode 1004. Again, the TMS/TCK 624 signal operatesas the TCK input to the selected Tap domain and TCK/TMS 622 operates asthe TMS input to the selected Tap domain. Also again, the delay 1212between the TCK/TMS and TMS/TCK signals causes all rising edgetransitions on the TCK/TMS signal 622 to occur while the TMS/TCK signal624 is at a logic low level, forcing non-selected Tap domains 602 toremain the Run Test/Idle state.

Timing example 1206 of FIG. 12 shows the Tap controller 104 statesequence of a data register scan operation being used to set the SwitchControl signal 614 of the selected Tap domain 602 low to switch from thedirect scan access mode 1004 to the daisy-chain scan access mode 1002.Again, the Pause indication 1210 in the Run Test/Idle state is where theJTAG controller 716 sets the control signal 740 low to allow outputtingthe daisy-chain scan access TCK and TMS protocol to all Tap domains 602.

FIG. 13 depicts an example of an IEEE 1149.1 Tap domain 1302 which hasbeen extended to include Auxiliary Analog Circuitry 1304 and auxiliaryterminals AX1 1306 and AX2 1308. The AX1 1306 and AX2 1308 terminals arecoupled to the Auxiliary Analog Circuitry 1304. While only two auxiliaryterminals (AX1 and AX2) are shown, any number could be used. As seen,the Auxiliary Analog Circuitry may be coupled to the Tap control bus 136and instruction register control bus 138 to allow data registers withinthe Auxiliary Analog Circuitry to be accessed via the TDI 116 and TDO132 terminals to load/unload data and/or control information. Tapdomains are extended to include Auxiliary Analog Circuitry and terminalsto enable analog testing functions. One example of using AuxiliaryAnalog Circuitry and terminals with a Tap domain is given in IEEEstandard 1149.4 (Ref 3). With the exception of the Auxiliary AnalogCircuitry and terminals, the Tap domain 1302 is similar to Tap Domain102.

FIG. 14A depicts an example scan path 1402 where a number of Tap domain1302 interfaces of ICs/cores 1404-1410 are connected together serially,via their TDI 116 and TDO 132 terminals. The TDO input 312 and TDOoutput 314 of the scan path 1402, along with the TCK 120, TMS 124, TRST128, AX1 1306, and AX2 1308 terminals of each Tap Domain 1302, areconnected to an Extended Analog JTAG Controller 1416. The JTAGController 1416 can serve as a test, debug, trace, emulation,in-system-programming, analog test, and/or other application controller.

FIG. 14B depicts an example of an Extended Analog JTAG Controller 1416.The JTAG Controller consists of a Tap interface circuit 1418 and acomputer 320 for controlling the Tap interface circuit. The Tapinterface circuit 1418 is like the Tap interface circuit 318 except thatit includes AX1 1420 and AX2 142 terminals for interfacing to the AX11306 and AX2 1308 terminals of Tap domains 1302, and an AnalogSource/Destination circuit 1424. The Analog Source/Destination Circuit1424 is used to control the inputting and/or outputting of analogcurrent and/or voltage test signals between the controller's AX1 1420and AX2 1422 terminals and the AX1 1306 and AX2 1308 terminals ofAuxiliary Analog Circuitry of the Tap domains 1302. The input and/oroutput operation of the Analog Source/Destination Circuit 1424 iscontrolled by computer 320 via Control Circuitry 1432.

As seen in FIG. 14A, the Extended Analog JTAG controller 1416 cancommunicate to the Tap domains 1302 using JTAG instruction and datascans, as does the JTAG controller 316 of FIG. 3A. Also, the ExtendedAnalog JTAG controller 1416 can communicate voltage and/or current testsignals to the Auxiliary Analog Circuitry 1304 of Tap domains 1302 viathe AX1 and AX2 terminals 1420 and 1422. The analog voltage and/orcurrent test signals can be used to test analog circuitry internal tothe IC/core or external of the IC/core. Examples of such analog testingare described in detail in IEEE standard 1149.4.

FIG. 15 depicts an example of an IEEE 1149.1 Tap domain 1502 of thepresent embodiment. Tap domain 1502 is like the Tap domain 1302 of FIG.13 with the following differences.

The TCK 120, TMS 124, AX1 1306, and AX2 1308 terminals of FIG. 15 havebeen renamed to TCK/TMS 622, TMS/TCK 624, AX1/TDI 1526, and AX2/TDO1528, respectively, to indicate the dual use of the terminals.

A two input multiplexer 604 has been inserted into the TCK/TMS 622 inputpath to the Tap controller 104 and coupled to buffer 122, buffer 126,Switch control signal 614, and the TCK input of Tap controller 104 asdescribed in FIG. 6.

A two input multiplexer 606 has been inserted into the TMS/TMS 624 inputpath to the Tap controller 104 and coupled to buffer 122, buffer 126,Switch control signal 614, and the TCK input of Tap controller 104 asdescribed in FIG. 6.

A two input multiplexer 1504 and 3-state buffer 1506 have been added.One input of multiplexer 1504 is coupled to the previously described TDOoutput enable signal 632, the other input is coupled to the previouslydescribed OFF signal 630, and the output of the multiplexer is coupledto the 3-state input of buffer 1506. The OFF signal is set to a statethat disables the output of buffer 1506. The control input to themultiplexer is connected to the previously described switch controlsignal 614. The input of buffer 1506 is coupled to the output of TDOoutput register 114, and the output of the buffer is coupled to AX2/TDOterminal 1528.

A two input multiplexer 616 has been inserted into the TDI input path116 and a buffer 1508 has been added. The input of buffer 1508 iscoupled to the AX1/TDI terminal 1526 and the output of the buffer iscoupled to an input of multiplexer 616. The other input of multiplexer616 is coupled to the output of TDI buffer 118, and the output of themultiplexer is coupled to the TDI inputs of the instruction register 106and data registers 108. The control input to the multiplexer isconnected to the previously described switch control signal 614.

In the Tap domain 1502 example of FIG. 15 it is seen that when theswitch control signal 614 is set low, multiplexer 604 couples theTCK/TMS terminal 622 to the TCK input of Tap controller 104, multiplexer606 couples the TMS/TCK terminal 624 to the TMS input of Tap controller104, multiplexer 1504 couples the OFF signal to the 3-state controlinput of AX2/TDO buffer 1506, and multiplexer 616 couples the output ofthe TDI input buffer 118 to the TDI inputs of the data registers 108 andinstruction register 106. In this configuration, the Tap domain 1502operates the same as the Tap domain 1302 of FIG. 13.

When the switch control signal 614 is set high, multiplexer 604 couplesthe TMS/TCK signal 624 to the TCK input of Tap controller 104,multiplexer 606 couples the TCK/TMS signal 622 to the TMS input of Tapcontroller 104, multiplexer 1504 couples the TDO output enable signal632 to the 3-state input of AX2/TDO buffer 1506, and multiplexer 616couples the output of AX1/TDI buffer 1508 to the TDI inputs of the dataregisters 108 and instruction register 106. In this configuration, theTap domain 1502 departs from the operation mode of Tap domain 1302 ofFIG. 13 and enters the direct scan access operation mode of the presentembodiment.

FIG. 16A depicts an example scan path 1602 where a number of Tap domain1502 interfaces of ICs/Cores 1604-1610 are connected together serially,via their TDI 116 and TDO 132 terminals. The TDO input 312 and TDOoutput 314 of the scan path 1602, along with the TCK/TMS 622, TMS/TCK624, TRST 128, AX1/TDI 1526, and AX2/TDO 1528 terminals of each TapDomain 1502, are connected to an Extended Analog JTAG Controller withDirect Scan Access 1616. The JTAG Controller 1616 can serve as a test,debug, trace, emulation, in-system-programming, analog testing, and/orother application controller. The JTAG controller 1616 can access theseapplications using the conventional JTAG daisy-chain approach or thedirect scan access approach of the present embodiment.

FIG. 16B depicts an example of an Extended Analog JTAG Controller withDirect Scan Access 1616. The JTAG Controller 1616 consists of a Tapinterface circuit 1618 and a computer 320 for controlling the Tapinterface circuit. The Tap interface circuit 1618 is the like the Tapinterface circuit 1418 of FIG. 14B with the following differences.

The TCK 322, TMS 326, AX1 1420, and AX2 1422 terminals of the controllerof FIG. 14B have been renamed to TCK/TMS 724, TMS/TCK 726, AX1/TDO 1620,and AX2/TDI 1622, respectively, to indicate the dual use of theterminals. The TCK/TMS terminal 724 couples to the TCK/TMS terminals 622of Tap domains 1502. The TMS/TCK terminal 726 couples to the TMS/TCKterminals 624 of Tap domains 1502. The AX1/TDO terminal 1620 couples tothe AX1/TDI terminals 1526 of Tap domains 1502. The AX2/TDI 1622terminal couples to the AX2/TDO terminals 1528 Tap domains 1502. The TDO334, TDI 338, and TRST 330 terminals are coupled to Tap Domain 1502terminals TDI 116, TDO 132, and TRST 128 respectively.

A two input multiplexer 728 has been inserted into the TCK/TMS 724output path as described in FIG. 7B.

A two input multiplexer 730 has been inserted into the TMS/TCK 726output path as described in FIG. 7B.

A two input multiplexer 732 has been inserted into the TDI 338 inputpath as described in FIG. 7B.

A buffer 1628 has been added. The input of the buffer is coupled to theAX2/TDI terminal 1622 and the output of the buffer is coupled to aninput of multiplexer 732.

A 3-state buffer 1626 has been added. The input of the buffer is coupledto the output of TDO source 336, the output of the buffer is coupled tothe AX1/TDI terminal 1620, and the 3-state control input of the bufferis coupled to the previously described control signal 740.

Control Circuitry 1624 provides, in addition to the functionality ofControl Circuitry 1432, the control signal 740 for regulating thesettings of multiplexers 728-732 and buffer 1626, in response to inputfrom computer 320.

In the Tap interface circuit 1618 example of FIG. 16, when the controlsignal 740 is set low the multiplexers 728-732 are controlled such thatthe TCK source 324 is coupled to the TCK/TMS terminal 724, the TMSsource 328 is coupled to the TMS/TCK terminal 726, the TDI Destination340 is coupled to the TDI terminal 338, and the AnalogSource/Destination 1624 is the only source for AX1/TDO terminal 1620. Inthis mode, the Tap Interface Circuit 1618 operates the same as the TapInterface Circuit 1418 of FIG. 14B to access the Tap domains in adaisy-chain fashion and perform analog test operations.

When the control signal 740 is set high the multiplexers 728-732 arecontrolled such that the TMS source 328 is coupled to the TCK/TMSterminal 724, the TCK source 324 is coupled to the TMS/TCK terminal 726,the TDI Destination 340 is coupled to the AX2/TDI terminal 1622, and theTDO source 336 is coupled to the AX1/TDO terminal 1620. In this mode,the Tap Interface Circuit 1618 operates to access the selected Tapdomain 1502 using the direct scan access approach of the presentembodiment. The selected Tap domain 1502 will be configured for directscan access by its Switch Control signal 614 being set high.Non-selected Tap domains 1502 will remain in the daisy-chain TDI to TDOaccess mode by their Switch Control signal 614 being set low.

During direct scan access, the selected Tap domain 1502 will inputserial data at its AX1/TDI terminal 1526 from the AX1/TDO terminal 1620of JTAG controller 1616, and will output serial data from its AX2/TDOterminal 1528 to the AX2/TDI terminal 1622 of the JTAG controller 1616during instruction and data scan operations. As described previously inregard to FIGS. 7A-7C, only the selected Tap domain will receive thecorrect TMS and TCK inputs for performing instruction and data scans.Non-selected Tap domains will receive input on TMS and TCK but the inputwill not affect the state of the non-selected Tap domains.

By substituting IC/cores 1604-1610 for IC/cores 704-710 and the JTAGcontroller 1616 for JTAG controller 716 in FIGS. 8 and 9A-9B, use of thepresent embodiment to perform direct scan access operations usingauxiliary analog terminals can be seen. Also, the transition betweendaisy-chain access mode and direct scan access modes is the same as wasdescribed previously in regard to in FIGS. 10-12.

FIG. 17 depicts a first alternate Tap domain 1702 implementation of thepresent embodiment. The Auxiliary Digital or Analog Circuitry andInterface block 1704 of FIG. 17 represents either the Auxiliary DigitalCircuit block 404 and interface of FIG. 6 or the Auxiliary AnalogCircuit block 1304 and interface of FIG. 15. Connections 614, 1706,1708, and 1710 to block 1704 represent the connections to the AuxiliaryDigital or Analog Circuits blocks and interfaces of FIGS. 6 and 15.AX1/TDI 1718 represents either AX1/TDI 626 of FIG. 6 or AX1/TDI 1526 ofFIG. 15. AX2/TDO 1720 represents either AX2/TDO 628 of FIG. 6 or AX2/TDO1528 of FIG. 15. The Tap domain 1702 is like the Tap domains 602 of FIG.6 and 1502 of FIG. 15 with the following difference.

Instead of using a single Tap controller 104 and multiplexers 604 and606, the implementation of FIG. 17 uses two Tap controllers 104 and 1714and one multiplexer 1716. Tap controller 1714 is different from Tapcontroller 104 in that it has an enable (EN) input. The TCK and TMSinputs of Tap controller 104 are coupled to TCK/TMS 622 and TMS/TCK 624terminals respectively, and the TCK and TMS inputs of Tap controller1714 are coupled to the TMS/TCK 624 and TCK/TMS 622 terminalsrespectively. The TRST input of both Tap controllers are coupled to theTRST terminal 128. The enable input of Tap controller 1714 is coupled tothe switch control signal 614. The multiplexer 1716 has a first businput coupled to receive the control bus output 136 from Tap controller104, a second bus coupled to receive the control bus output 136 from Tapcontroller 1714, an output bus 1720 for outputting a selected one of theTap control buses 136, and a control input coupled to switch controlsignal 614.

At power up or following a test reset, the switch control signal 614will go low as it does for the Tap domains 602 and 1502. While switchcontrol 614 is low, multiplexer 1714 selects the control output bus 136of Tap controller 104 to be coupled to bus 1720. While switch controlsignal 614 is low, the enable input of Tap controller 1714 is lowforcing Tap controller 1714 to be disabled in the Run Test/idle state ofits state diagram 1802, as shown in FIG. 18. In this mode, the Tapdomain 1702 can operate, via Tap controller 104, in the TDI to TDOdaisy-chain scan path arrangement of FIG. 8 with the JTAG controller 716set for daisy-chain scan access (i.e. JTAG controller control signal 740set low).

When switch control signal 614 is set high, via a data or instructionscan, Tap controller 1714 is enabled, via its enable input being high,and its control output bus 136 is coupled to bus 1720 via multiplexer1716. As seen in FIG. 18, Tap controller 1714 is enabled in the RunTest/Idle state which is the correct state for taking over control ofbus 1720 from Tap controller 104 and operating the Tap domain 1702 inthe direct scan access mode (see FIGS. 10, 11, and 12). In this mode,the Tap domain 1702 can operate in the direct scan access arrangementsof FIGS. 9A-9D with the JTAG controller 716 set for direct scan access(i.e. JTAG controller control signal 740 set high). While the JTAGcontroller is set for direct scan access, Tap controller 104 willreceive the previously described incorrect TCK and TMS protocol whichcauses it to remain in the Run Test/Idle state. The daisy-chain scanaccess mode may be re-entered by performing a data or instruction scanand setting the switch control signal 614 low, as described in regard toFIGS. 10-12.

FIG. 19 depicts a second alternate Tap domain 1902 implementation of thepresent embodiment. The Tap domain 1902 is like the Tap domain 1702 withthe following difference.

Instead of using two Tap controllers 104 and 1714 and multiplexer 1716,the implementation of FIG. 19 uses one Tap controller 104, onemultiplexer 1906, and two TMS input terminals (TMS1, TMS2) 1908 and1910. One input of multiplexer 1906 is coupled to TMS0 terminal 1908,the other input is coupled to TMS1 terminal 1910, and the multiplexeroutput is coupled to the TMS input of Tap controller 104. The controlinput of multiplexer 1906 is coupled to switch control signal 614. TheTMS0 terminal 1908 is the normal JTAG TMS terminal used to perform scanaccess operations via TDI 116 and TDO 132 (as does TMS terminal 124 ofFIG. 1) and the TMS1 terminal 1910 is an additional TMS terminal used toperform direct scan access operations via AX1/TDI 1718 and AX2/TDO 1720.

At power up or following a test reset, the switch control signal 614will go low as it does for the Tap domains 602, 1502, and 1702. Whileswitch control 614 is low, multiplexer 1906 selects TMS0 1908 to becoupled to the TMS input of Tap controller 104. In this mode, the Tapdomain 1902 can operate in response to input from TMS0 terminal 1908 toperform daisy-chain instruction and data scan operations from TDI 116 toTDO 132 as per FIG. 5A.

When switch control signal 614 is set high, via a data or instructionscan, multiplexer 1906 couples the TMS1 terminal 1910 to the TMS inputof Tap controller 104. In this mode, the Tap domain 1902 can operate inresponse to input from TMS1 terminal 1910 to perform direct scan accessinstruction and data scan operations from AX1/TDI 1718 to AX2/TDO 1720.

FIG. 20A depicts a scan path 2002 of IC/cores 2004-2010, each having aTap domain 1902. The scan path 2002 is coupled to an ExtendedDigital/Analog JTAG Controller with Direct Scan Access 2016.

In FIG. 20B the JTAG controller 2016 is seen to include a Tap interfacecircuit 2018, and a computer 320. The JTAG controller's TCK 322, TMS02026, TMS1 2028, TRST 330, TDO 334, TDI 338, AX1/TDO 2022, and AX2/TDI2024 terminals are connected to the 1902 Tap domain's TCK 120, TMS01908, TMS1 1910, TRST 128, TDI 116, TDO 132, AX1/TDI 1718, and AX2/TDO1720 terminals, respectively. A Digital or Analog Source/Destinationblock 2020 is shown in Tap interface circuit 2018 to indicate use ofeither the Auxiliary Digital Circuit block and interface of FIG. 7B orthe Auxiliary Analog Circuit block and interface of FIG. 16B. Alsocontrol circuit 2032 could be either control circuit 738 of FIG. 7B orcontrol circuit 1628 of FIG. 16B. Circuit block 2020 is coupled to thecontrol signal 740, multiplexer 732, and TDO Source 336, as shown inFIGS. 7B and 16B. The Tap interface circuit 2018 includes ademultiplexer 2030. The input of the demultiplexer is coupled to the TMSsource 328, one output is coupled to TMS0 2026, the other output iscoupled to TMS1 2028, and the control input is coupled to control signal740.

If the Tap domains 1902 of scan path 2002 are set for daisy-chain scanaccess via TDI 312 and TDO 314 (their switch control signal 614 is low)the control signal 740 of the Tap interface circuit 2018 will be low toallow TMS source 328 to drive the Tap domain TMS0 terminals 1908 (viademultiplexer 2030 and TMS0 terminal 2026) while the scan path TDIterminal 312 inputs from TDO terminal 334 and the scan path TDO terminal314 outputs to the TDI terminal 338.

If a Tap domain 1902 of scan path 2002 is set for direct scan access viaAX1/TDI 1718 and AX2/TDO 1720 (its switch control signal 614 is high)the control signal 740 of the Tap interface circuit 2018 will be high toallow TMS source 328 to drive the Tap domain's TMS1 terminal 1910 (viademultiplexer 2030 and TMS1 terminal 2028) while the Tap domain'sAX1/TDI terminal 1718 inputs from AX1/TDO terminal 2022 and the Tapdomain's AX2/TDO terminal 1720 outputs to the AX2/TDI terminal 2024.

So as seen in FIGS. 19, 20A, and 20B, the TMS0 terminals of the Tapdomains 1902 and JTAG controller 2016 are used during daisy-chain scanaccess operations of the Tap domains in scan path 2002 whereas the TMS1terminals of the Tap domains 1902 and JTAG controller 2016 are usedduring direct scan access operations to a selected Tap domain in scanpath 2002.

FIG. 21 depicts a third alternate Tap domain 2102 implementation of thepresent embodiment. The Tap domain 2102 is like the Tap domains 1702 and1902 with the following differences.

(1) Instead of using two Tap controllers 104 and 1714 and multiplexer1716 as in FIG. 17 or a single Tap controller 104 and TMS multiplexer1906 as in FIG. 19, the implementation of FIG. 19 uses one Tapcontroller 104 with direct connections to terminals TCK 120, TMS 124,and TRST 128.

(2) A two input multiplexer 2104 has been inserted in the TDO 132 outputpath. One input of the multiplexer is coupled to the output of TDIbuffer 118, the other input is coupled to the output of TDO register118, the output of the multiplexer is coupled to the input of TDO buffer134, and the control input is coupled to switch control signal 614. Thecoupling between the output of TDI buffer 118 and the input ofmultiplexer 2104 can be either a direct connection as indicated bydotted line 2108 or it can be coupled through a storage element such asdotted line DFF register 2108. If coupled using register 2108, theregister will be connected to the output control bus 136 of Tapcontroller 104 in such a way as to allow the register to shift data fromTDI 116 to TDO 132 during both instruction and data scan operations. Ascan be seen, while switch control signal 614 is high (i.e. direct scanaccess mode), and during instruction and data scan operations theregister 2106 or connection 2108 provides a bypass path around the Tapdomain's instruction 106 and data 108 registers from TDI 116 to TDO 132.

At power up or following a test reset, the switch control signal 614will go low as it does for the Tap domains 602, 1502, 1702, and 1902.While switch control 614 is low, Auxiliary Digital or Analog Circuitblock 1704 is enabled to perform its designated digital I/O (such asIEEE 5001) or analog I/O (such as IEEE 1149.4) functions. Also whileswitch control signal 614 is low, multiplexer 2104 couples the output ofTDO register 114 to the TDO output terminal 132 to allow Tap controller104 to perform instruction and data scan operations from TDI 116 to TDO132.

When switch control signal 614 is set high, via a data or instructionscan, the designated function of the Auxiliary Digital or Analog Circuitblock 1704 is disabled to allow the Tap controller 104 to perform directaccess instruction or data scan operations using the Auxiliary circuitblock's AX1/TDI 1718 and AX2/TDO 1720 terminals. While switch controlsignal 614 is high, multiplexer 2104 is set to pass data from TDI 116 toTDO 132, via either the direct connection 2108 or register 2106, duringdirect scan access instruction and data scan operations. So, duringdirect access instruction or data scan operations, Tap domain 2102shifts data simultaneously through two separate paths, one path from TDI116 to TDO 132 and the other path from AX1/TDI 1718 to AX2/TDO 1720.

FIG. 22A depicts a scan path 2202 of IC/cores 2204-2210, each having aTap domain 2102. The scan path 2202 is coupled to an ExtendedDigital/Analog JTAG Controller with Simultaneous Daisy-Chain and DirectScan Access 2220.

In FIG. 22B the JTAG controller 2220 is seen to include a Tap interfacecircuit 2222, and a computer 320. The JTAG controller's TCK 322, TMS326, TRST 330, TDO 334, TDI 338, AX1/TDO 2022, and AX2/TDI 2024terminals are connected to the 2102 Tap domain's TCK 120, TMS 124, TRST128, TDI 116, TDO 132, AX1/TDI 1718, and AX2/TDO 1720 terminals,respectively. As with Tap interface circuit 2018 of FIG. 20B, the Tapinterface circuit 2222 includes a Digital or Analog Source/Destinationand interface block 2020 to indicate use of either the Auxiliary Digital524 or Analog 1624 Circuit blocks and interfaces of FIGS. 7B and 16B.The Tap interface circuit 2018 differs from previous Tap interfacecircuits in that it includes a plural TDO sources 2216 and a plural TDIdestinations 2218.

The plural TDI sources 2216 and TDO destinations 2218 are coupled tocontrol circuitry 2224 which has been adapted to allow computer 320 tocontrol the sources and destinations 2216 and 2218. One TDO output 2226of the plural TDO sources 2216 is coupled to the TDO terminal 338 andthe other TDO output 2212 is coupled to the AX1/TDO terminal 2022 viacircuit 2020. One TDI input 2228 of the plural TDI destinations 2218 iscoupled to the TDI terminal 338 and the other TDI input 2214 is coupledto the AX2/TDI terminal 2024 via circuit 2020.

If the Tap domains 2102 of scan path 2202 in FIG. 22A are set fordaisy-chain scan access via TDI 312 and TDO 314 (i.e. their switchcontrol signal 614 is low), the control signal 740 of the Tap interfacecircuit 2222 in FIG. 22B will be set low to de-couple the TDO signal2212 from the AX1/TDO 2022 terminal and the TDI signal 2214 from theAX2/TDI 2024 terminal, which enables circuit 2020 to perform digital I/O(such as IEEE 5001) or analog I/O (such as IEEE 1149.4) operations.During daisy-chain scan access, the TCK source 322 drives the TCK 120terminals of Tap domains 2102, the TMS source 328 drives the TMSterminals of Tap domains 2102, the 2226 output of plural TDO sources2216 inputs data to the TDI 312 input of scan path 2202, and 2228 inputof the Plural TDI destinations 2218 inputs data from the TDI 314 outputof scan path 2202. Also during daisy-chain scan access, output 2212 ofthe TDO sources 2216 and input 2214 of the TDI destinations 2218 aredisabled by control circuitry 2224 since access to the AX1/TDI 2020 andAX2/TDI 2022 terminals of circuit block 2020 is not available.

FIG. 23A depicts JTAG instruction or data scan operations occurring onscan path 2202 while it is in the above mentioned daisy-chain scanaccess mode. As seen the AX1/TDO 2022 and AX2/TDI 2024 terminals arefree to perform their designated digital or analog I/O operations.

In Figure If a Tap domain 2102 of scan path 2202 in FIG. 22A is set fordirect scan access via AX1/TDI 1718 and AX2/TDO 1720 (i.e. its switchcontrol signal 614 is high), the control signal 740 of the Tap interfacecircuit 2222 in FIG. 22B will be set high to couple the TDO signal 2212to the AX1/TDO 2022 terminal and the TDI signal 2214 to the AX2/TDI 2024terminal. While control signal 740 is high, the digital I/O (such asIEEE 5001) or analog I/O (such as IEEE 1149.4) operations of circuit2020 are disabled and the circuit's AX1/TDI and AX2/TDI terminals can beused for direct scan access input and output to the selected Tap domain.During direct scan access, the TCK source 322 drives the TCK 120terminals of Tap domains 2102, the TMS source 328 drives the TMSterminals of Tap domains 2102, the AX1/TDO 2022 terminal of circuit 2020outputs data from TDO sources 2216 (via output 2212) to the AX1/TDIterminal 1718 of the selected Tap domain, and the AX2/TDI terminal 2024of circuit 2020 inputs data to TDI sources 2218 (via input 2214) fromthe AX2/TDO terminal 1720 of the selected Tap domain.

Also during direct scan access, output 2226 of TDO sources 2216 outputsdata (via TDO 334) to the TDI 312 input of scan path 2202 and input 2228of TDI destinations 2218 inputs data (via TDI 338) from the TDO 314output of scan path 2202. From this description it is seen that duringdirect scan access operations the JTAG controller 2220 simultaneouslyscans data through the scan path 2202 from TDO 334 to TDI 338 andthrough the selected Tap domain from AX1/TDO 2022 to AX2/TDI 2024.

FIG. 23B depicts daisy-chained JTAG instruction or data scan operationsoccurring in the Tap domains 2102 of IC/cores 2204-2210 from TDI 312 toTDO 314 of scan path 2202, while Tap domain 2102 of IC/core 2208 is inthe direct scan access mode and simultaneously performing instruction ordata scan operations from its AX1/TDI 1718 and AX2/TDO 1720 terminals.In IC/core 2208, the TDI to TDO bypass path, formed using either adirect connection 2108 or register bit 2106 as described in FIG. 21,provides the serial link between the daisy-chained Tap domains ofIC/cores 2204, 2206, and 2210. As seen in FIG. 23B, the AX1/TDO 1718 andAX2/TDI 1720 terminals of IC/cores 2204, 2206, and 2210 are disabled(dotted line) to allow the JTAG controller 2220 to serially input to andoutput from the AX1/TDI 1718 and AX2/TDO 1720 terminals of the selectedTap domain of IC/core 2208.

During JTAG instructions scan operations to the Tap domains in the scanpath 2202 of FIG. 23B, the instruction registers 106 of thedaisy-chained IC/cores 2204, 2206, and 2210 are loaded from the JTAGcontroller 2220 using the TDI 312 and TDO 314 scan path terminals, andthe instruction register 106 of the directly accessed IC/core 2208 isloaded from the JTAG controller 2220 using the IC/core 2208 AX1/TDI 1718and AX2/TDO 1720 terminals. The length of the instruction scan operationperformed by the JTAG controller 2220 is set by the longer of thedaisy-chained instruction registers in IC/core 2204, 2206, and 2210 orthe directly accessed instruction register in IC/core 2208.

For example, if the length of the daisy-chained instruction registers is500 bits (including register bit 2106 of IC/core 2208 if implemented)and the length of the directly accessed instruction register of IC/core2208 is 10 bits, the JTAG controller will perform an instructionregister scan operation of 500 bits. During the instruction registerscan operation, the JTAG controller will input the 500 bit instructionscan pattern to the daisy-chained instruction registers of IC/cores2204, 2206, and 2210 via TDI 312 and TDO 314, and a 500 bit instructionscan pattern to the directly accessed instruction register of IC/core2208. The 10-bit instruction for the directly accessed IC/core 2208 willbe positioned at the end of the 500 bit instruction scan pattern shiftedinto the instruction register of IC/core 2208 so that it loads correctlyinto the 10-bit instruction register.

The daisy-chained Tap domains 2102 of IC/cores 2204, 2206, and 2210 willbe loaded with a JTAG Bypass, Clamp, or HighZ instruction to allow thesingle bit JTAG Bypass Register of the Tap domains to be selected inscan path 2202 during JTAG data register scan operations. Selecting theBypass Register in IC/cores 2204, 2206, and 2210 allows scanning don'tcare bits through the daisy-chained scan path 2202 from TDI 312 to TDO314. Also, selecting the Bypass Register of IC/cores 2204, 2206, and2210 allows the length of the data scan operation to be set to the bitlength of the data register being directly accessed in IC/core 2208.

For example, if the data register being directly accessed in IC/core2208 is 50 bits long, and the length of the daisy-chained BypassRegisters is 200 bits long, the data register scan operation can be setto 50 bits to match the length of the directly accessed data register ofIC/core 2208. Alternately, if the data register being directly accessedin IC/core 2208 is 200 bits long, and the length of the daisy-chainedBypass Registers is 50 bits long, the data register scan operation canbe set to 200 bits, again to match the length of the directly accesseddata register of IC/core 2206. This under-scanning or over-scanning ofdaisy-chained Bypass registers does not effect IC/cores 2204, 2206, 2210since, as mentioned, the data scanned into Bypass registers is don'tcare data.

In summarizing the differences among the embodiments of the presentdisclosure it is seen that:

(1) Tap domain 602 of FIG. 6 can selectively operate in daisy-chained ordirect scan access modes by reversing the TCK and TMS input terminalconnections to the Tap domain's Tap controller 104, and reusingauxiliary digital terminals for direct scan access TDI and TDO terminalsTap domain 602 requires a JTAG controller (like shown in FIG. 7B) thatcan reverse its TCK and TMS output terminals and reuse auxiliary digitalterminals for direct scan access TDI and TDO terminals.

(2) Tap domain 1502 of FIG. 15 can selectively operate in daisy-chainedor direct scan access modes by reversing the TCK and TMS input terminalconnections to the Tap domain's Tap controller 104, and reusingauxiliary analog terminals for direct scan access TDI and TDO terminals.Tap domain 1502 requires a JTAG controller (like shown in FIG. 16B) thatcan reverse its TCK and TMS output terminals and reuse auxiliary analogterminals for direct scan access TDI and TDO terminals.

(3) Tap domain 1702 of FIG. 17 can selectively operate in adaisy-chained mode using a first Tap controller 104 and in a direct scanaccess mode using a second Tap controller 1714. Like Tap domains 602 and1502, Tap domain 1702 reuses auxiliary digital or analog terminals fordirect scan access TDI and TDO terminals. Tap domain 1702 requires aJTAG controller (like shown in FIGS. 7B and 16B) that can reverse itsTCK and TMS output terminals and reuse auxiliary digital or analogterminals for direct scan access TDI and TDO terminals.

(4) Tap domain 1902 of FIG. 19 can selectively operate in daisy-chainedor direct scan access modes by using two separate TMS input terminals,and reusing auxiliary digital or analog terminals for direct scan accessTDI and TDO terminals. Tap domain 1902 requires a JTAG controller (likeshown in FIG. 20B) that has two separately controllable TMS outputterminals and can reuse auxiliary digital or analog terminals for directscan access TDI and TDO terminals.

(5) Tap domain 2102 of FIG. 21 can selectively operate in adaisy-chained or in a simultaneous daisy-chain and direct scan accessmodes. During the simultaneous daisy-chain and direct scan access mode,the daisy-chain access is achieved using the normal TDI and TDOterminals, while the direct scan access is achieved by reusing auxiliarydigital or analog terminals as additional TDI and TDO terminals. Tapdomain 2102 requires a JTAG controller (like shown in FIG. 22B) that hasa first TDO source for transmitting data to a first TDO terminal, asecond TDO source for transmitting data to an auxiliary digital oranalog terminal used as a second TDO terminal, a first TDI destinationfor receiving data from a first TDI terminal, and a second TDIdestination for receiving data from an auxiliary digital or analogterminal used as a second TDI terminal.

It should be noted that while the scan path examples of FIGS. 7A, 8,9A-9D, 16A, 20A, 22A, and 23A-23B show all the IC/cores in the scanpaths as being adapted to include one of the Tap domain embodiments ofthe present disclosure, that need not be the case. Indeed the scan pathsmay include mixtures of IC/cores with adapted and non-adapted Tapdomains. For example, in scan path 702 of FIG. 7A, IC/cores 704 and 710may include the non-adapted Tap domains 402 of FIG. 4 while IC/cores 706and 708 include the adapted Tap domains 602 of FIG. 6. Similarly, theother scan paths could contain mixtures of adapted Tap domains andnon-adapted Tap domains. The operation of the present embodiments toprovide direct scan access to a selected and adapted Tap domain in ascan path of Tap domains is independent of whether the scan pathincludes non-adapted Tap domains or not.

Although the present embodiments have been described in detail, itshould be understood that various changes, substitutions, andalterations may be made without departing from the spirit of thedisclosure.

What is claimed is:
 1. An integrated circuit comprising: (a) a serialinstruction register having a serial data input coupled to a test datainput, a serial data output, an instruction register control bus output,and a control bus input; (b) a serial data register having a serial datainput coupled to the test data input, a serial data output, and acontrol input coupled to the instruction register control bus output;(c) first multiplexer circuitry coupling the serial data output of theinstruction register and the serial data output of the data register toa test data output, and having a control input; (d) TAP controlcircuitry having a test clock input, a test mode select input, and a TAPcontrol bus output coupled to the control bus input of the instructionregister and the control input of the first multiplexer circuitry; (e)auxiliary circuitry coupled to the serial instruction register, the TAPcontrol circuitry, the test data input, the test data output, and havinga first control output, a first auxiliary input and a first auxiliaryoutput; (f) second multiplexer circuitry having an input coupled withthe control output of the auxiliary circuitry, an input coupled with theTAP control bus, a control input coupled with the instruction registercontrol bus output, and an output; (g) an input buffer having an inputcoupled to an auxiliary input and output lead and an output coupled withthe first auxiliary input; and (h) a tristate output buffer having aninput coupled with the first auxiliary output, an output coupled withthe auxiliary input and output lead, and a control input coupled withthe output of the second multiplexer.
 2. The integrated circuit of claim1 in which the auxiliary circuitry is one of a debug circuit, emulationcircuit, in-circuit programming circuit, I/O communication circuit,triggering circuit, and breakpoint circuit.
 3. The integrated circuit ofclaim 1 in which the auxiliary circuitry is a digital test circuit. 4.The integrated circuit of claim 1 in which the auxiliary circuitry is ananalog test circuit.